This invention relates mainly to an assistor for reducing stepping force of a clutch pedal for use in a medium-sized automobile.
As a conventional assistor for reducing stepping force of a medium-sized automobile, there has been deviced an assistor in which a helper spring has been tensely provided on a cluch pedal to reduce stepping force by a tension of the helper spring.
However, the helper spring has been tensely provided by means of a fulcrum-passing-over system such as that equipped in a stand of bicycle, so that there has been a disadvantage that it has had no effect of reducing stepping force but a required stepping force has inversely increased at the initial state of stepping a pedal.
Further, as shown in FIG. 5, a device has been developed; in which a hydraulic servo unit 54 has been disposed between a master cylinder 52 connected to a clutch pedal 51 and a slave cylinder 53 connected to a clutch in order to magnify hydraulic force by utilizing negative pressure from a negative-pressure source 55. However, the device shown in FIG. 5 has a complex construction including a large quantity of components resulting in a high manufacturing cost because it must be equipped with a hydraulic mechanism such as an oil passage etc. in the unit 54. Moreover, this device can be used only for a hydraulic type clutch pedal, and can not be used for a wire transmitting type cluch pedal.
An object of this invention is to provide an assistor for reducing stepping force which has a simple construction and can be manufactured at a low cost, and which can perform full stepping force reducing function.
Another object of this invention is to provide an assistor for reducing stepping force which can be utilized for pedals of both hydraulically transmitting type and wire transmitting type.
In order to accomplish the above objects in this invention, a push rod is inserted into an assistor casing freely movably in the axial direction, a casing outside end of the rod is interconnected to a clutch pedal, a casing inside portion of the rod is provided with a piston which divides the casing into a first chamber and a second chamber, the first chamber intercommunicates with atmosphere and the second chamber intercommunicates freely changeably with atmosphere and a negative pressure source through a change-over valve mechanism, and the piston is interlocked with the change-over valve mechanism through the means of a negative-pressure setting spring so that negative pressure for reducing stepping force can be fed into the second chamber according to a shifted length of the rod.